It is known in the art to power an apparatus by coupling the apparatus to a drive component of a machine via a rotational coupling. For instance, a pump, such as fuel or oil pump, can be coupled to a rotating crank shaft of an engine via a rotational coupling. Often, a drive gear is coupled to rotate with the crank shaft of the engine. The rotational coupling can include a gear that is meshed to rotate with the drive gear directly or via intervening idler gears. The torque from the rotating gear of the rotational coupling can be transferred to a pump shaft through a variety of ways known in the art. Thus, when the gear rotates, opposing surfaces of the gear and the pump shaft cause the torque from the rotating gear to rotate the shaft. However, if the pump seizes for any reason, such as a bearing failure, the pump's resistance to rotation will be transferred to the gear via the opposing surfaces. The resistance can be transferred back to the crank shaft, and possibly damage the engine.
It is known in the art that breaking the coupling between the engine and the pump in the event of pump seizure can reduce the likelihood of engine damage. There are various known methods of breaking the coupling. For instance, a shear pin can be used to attach the pump shaft to the gear. The force created by the pump shaft seizing while the gear continues to be rotated will break the shear pin, and thus, disengage the coupling between the shaft and the gear. Another method known in the art for breaking the coupling in the event of pump seizure includes a threaded hub shrink fitted onto a stud of the pump shaft. The gear is attached to the threaded hub via an internal threaded portion of the gear. The gear is torqued onto the threaded hub in an opposite direction to the gear's drive rotation. If the drive torque is greater than the gear assembly torque, such as when the pump seizes, the gear becomes loose on the threads and drives itself towards the pump housing and out of mesh with the drive gear.
Although both the shear pin and the threaded hub can break the coupling between the pump shaft and the gear when the pump seizes, there is room for improvement. Engineers have found reliability issues with the shear pins. For instance, during normal operation of the rotational coupling, the shear pin is subjected to wear that can lead to premature failure of the shear pin, and thus, de-coupling of the pump shaft from the gear when there has been no pump seizure. In addition, the manufacturing costs of the threaded hub are unacceptably high. Moreover, with the threaded hub design, when the coupling is broken in an over-torque situation, the gear becomes out of mesh with the drive gear. The misalignment of the gears can cause the edges of the gears to run past one another, resulting in damage to the gears. Further, if the gear of the rotational coupling is an intermediate gear between the crank shaft and another gear driven apparatus, the operation of the other gear driving apparatus could also seize due to the pump seizure.
The present invention is directed at overcoming one of more of the problems set forth above.